The reaction of amines with polycarboxylic acids such as dibasic acids has long been known and takes place spontaneously at elevated temperatures with the evolution of water. As previously practiced, the second carboxyl group of the dibasic acid can react with the amine reactant such that a large amount of the amine is taken up by the amidation of both carboxyl groups of the dibasic acid thereby providing a mixture of monoamido carboxylic acid and N,N'-disubstituted diamide. A typical example of such a reaction is found in U.S. Pat. No. 2,604,449 to Bryant et al wherein amines are reacted with dibasic acids such as itaconic acid, adipic acid, succinic acid, azelaic acid, sebacic acid, and malonic acid. Approximately equal molar amounts of dibasic acids are shown to react with primary or secondary amines. The resulting reaction product is incorporated into lubricant compositions or greases for industrial purposes. Such purposes do not require high purity and therefore no accounting for the formation of diamide compounds was made.
Previously it was known to prepare monoamido derivatives of polycarboxylic acids by reacting the anhydride or esterified form of the polycarboxylic acid with an amine, obtaining an amido ester and then saponifying the ester group to provide a monoamido carboxylic acid. Such a process is disclosed in U.S. Pat. No. 2,191,738 to Balle. It is noted therein that the condensation of amines with polycarboxylic acids may be carried out by simply heating the two components with an excess of the acid deriviative until the reaction is complete. While no recognition of the formation of diamide and polyamide compounds is made, there is reference to the removal of insoluble byproducts in the examples.
A recent patent, U.S. Pat. No. 4,634,551 to Burns et al, describes novel, relatively stable and high melting crystalline amide peracids generically described as fatty peroxyacids having amide moieties in the fatty chain. An important feature of these compounds, as well as any other peracid, is their high purity, i.e., the absence of any impurities such as N'N'-disubstituted diamides in the case of amide peracids. Generally, the precursors of these amide peracids, that is, the amide acids, were reported to have been prepared by the reaction of the appropriate acid chloride with the appropriate amine followed by precipitation of the resulting amido acid. These compounds are said to have utility in detergent compositions as bleaching agents. The use of said compounds in detergent compositions requires large amounts of highly purified precursor materials from which the amide peracids may be prepared.
There is therefore needed a convenient, efficient process for the preparation of large amounts of monoamido acids in such high degree of purity, that amide peracids may be prepared which are stable and useful in detergent compositions. However, in the experience of the present inventor, it has been found that the known reactions of amines with polycarboxylic acids results in the production of large amounts of diamide and polyamide compounds rendering the process relatively inefficient. Several attempts to prepare monoamido polycarboxylic acids through derivatives of the acid have resulted in some refinements such as is described in co-pending application Ser. No. 826,555, filed Jan. 27, 1992 to Alul et al. The process of Alul et al, while found to be fairly efficient by means of the use of catalysts, employs as a starting material a diester of a dibasic acid, which is reacted with an akyl amine to produce the monoamido ester which is purified by distillation. To provide peroxy carboxylic acids, there is then required the hydrolysis of the other ester group. These reactions produce by-product alcohols and the need for purification of the disclosed monoamido carboxylic acid through acidification and filtration.
There is needed a direct process for producing the monoamido acid from the reaction of an amine and a dicarboxylic acid which avoids the production of large amounts of diamide compounds, as well as other by-products.